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CVE Record

CVE-2026-8948: Same-origin policy bypass in the DOM: Networking component

Same-origin policy bypass in the DOM: Networking component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.

CriticalCVSS 9.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysiscritical

Security readout for executives and security teams

Plain-English summary

This is a critical Mozilla browser and email-client flaw that could break same-origin protections, the boundary that stops one site or document from reading or changing another. The provided record says it was fixed in Firefox 151 and Thunderbird 151.

Executive priority

Prioritize remediation quickly on managed endpoints because this affects browser-origin trust and carries critical confidentiality and integrity impact. Current sources do not prove active exploitation, but the business risk is high enough to treat patch validation as urgent.

Technical view

CVE-2026-8948 is a same-origin policy bypass in Mozilla's DOM: Networking component. CVSS 3.1 is 9.1 with network attack vector, low complexity, no privileges, no user interaction, and high confidentiality and integrity impact. The bundle maps it to CWE-79 and CWE-942.

Likely exposure

Likely exposure is organizations running Mozilla Firefox or Thunderbird before the fixed advisory state. The bundle does not include exact vulnerable version ranges beyond stating the issue was fixed in Firefox 151 and Thunderbird 151, so asset/version validation is required.

Exploitation context

The source bundle does not show CISA KEV listing or cite active exploitation. It also does not provide exploit mechanics. Treat this as urgent because the impact is high and the attack vector is network-reachable, but do not claim exploitation without new evidence.

Researcher notes

Evidence is limited to public advisory metadata. The Bugzilla and advisory references identify a DOM: Networking same-origin policy bypass fixed in Firefox 151 and Thunderbird 151. Exact vulnerable ranges, exploit preconditions, and distribution-specific package status are not fully described in the provided bundle.

Mitigation direction

  • Update Firefox to the Mozilla-fixed release identified in the advisory.
  • Update Thunderbird to the Mozilla-fixed release identified in the advisory.
  • Check Mozilla advisories MFSA2026-46 and MFSA2026-50 for exact applicability.
  • Use enterprise software inventory to locate unmanaged Firefox or Thunderbird installations.
  • For Red Hat environments, review Red Hat CVE and VEX status before remediation planning.

Validation and detection

  • Inventory Firefox and Thunderbird versions across endpoints and servers.
  • Confirm installed versions align with Mozilla advisory fixed releases.
  • Review EDR, proxy, and browser telemetry for unusual cross-origin access indicators.
  • Check vulnerability scanner results against Mozilla and Red Hat advisories.
  • Document systems where version applicability is unclear and track vendor guidance.
Prepared
Confidence
medium
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-79: User-session and phishing behavior lookup

Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-942: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-8948 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Critical
CVSS
9.1 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
7Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: total

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
9.1CVSS 3.1CriticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N3.95.2CISA-ADP
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H1.65.9redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

9.1Critical
CVSS 3.1 vector shape for CVE-2026-8948Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
cvssV3_1other:ssvc
redhat-SADPfirefox: thunderbird: Same-origin policy bypass in the DOM: Networking component
other:Red Hat severity ratingcvssV3_1
  • 2026-05-19T14:01:58.864Z: Reported to Red Hat.
  • 2026-05-19T12:29:39.355Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MozillaFirefox151Listed
MozillaThunderbird151Listed
Weakness

CWE details

CWE-79CWE-942

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.